Evil geniuses who devise bombs to destroy things/people always have them detonate after at least an hour, giving the hero ample time to defuse it.
Bombs always have big, blinking, beeping timer displays. Evil geniuses who devise bombs to destroy things/people are always thoughtful enough to include a visible display (usually LED) of how much time remains before the bomb detonates, giving the hero accurate feedback on exactly how much time remains.
When you cut the wire to the detonator, the timer will stop. You will not be able to do this, however, until only one second remains.
All wires have different colors, so the hero can easily differentiate them when he has to cut the right one.
Bombs detonated with microwave ovens always explode 2 seconds after the timer reaches 00:00 and the microwave oven beeps (ex. "Under Siege").
Explosions always happen in slow motion. When an explosion occurs, make certain you are running away from the point of detonation so the blast can send you flying, in slow motion, toward the camera.
A building that in real life would require several dozen carefully placed explosive charges for demolition, can in a movie be destroyed by a single bomb in a car trunk (see "Lethal Weapon III"). This bomb will cause no damage to any other building on the block.
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